What is your routing table content?

For instane, if I want to add additional diagnostics controller to my EPiServer site I add following in Global.ascx.cs:

protected override void RegisterRoutes(RouteCollection routes)
{
    base.RegisterRoutes(routes);

    routes.MapRoute("AdditionalDiagnosticRoutes", 
                    "diag/{controller}/{action}/{param}", 
                    new { action = "Index", param = RouteParameter.Optional });
}

When I do this override and single step during debug it doesn't hit this class. My global.asax.cs class looks like this.

protected override void RegisterRoutes(System.Web.Routing.RouteCollection routes)
        {
            base.RegisterRoutes(routes);

            routes.MapRoute(
                "JsonGetX", // Route name
                "Surface/JsonGetX", // URL with parameters
                new { controller = "Surface", action = "JsonGetX" }
            );
        }

I have a controller that looks like this

public class SurfaceController : Controller
    {
        [HttpGet]
        public ActionResult JsonGetX()
        {
            return Json(new { Success = true }, JsonRequestBehavior.AllowGet);
        }

    }

    EDIT: I changed the routing to this so that we can exclude me doing wrong in the routing syntax

protected override void RegisterRoutes(RouteCollection routes)
        {
            base.RegisterRoutes(routes);

            routes.MapRoute(
                "JsonGetX", // Route name
                "Surface/{controller}/{action}/{param}", // URL with parameters
                new { action = "Index", param = RouteParameter.Optional }
            );
        }

If method is not hit then you can verify Global.asax file that you are really inheriting from your class:

<%@ Application Language="C#" Inherits="YourProject.Web.Global" %>

OK, where do I do write this?, If i put in my master page/ layout file (razor) I get an exception.

If you have Global.asax.cs file, there should be also Global.asax file, edit that. Note that if you double-click Global.asax file in VS - it still will open Global.asax.cs file :) Who needs to edit .asax file anyway, right!? :)

Thanks :) Don't know if this brings us closer to the problem but I changed to the path of my Global.asax.cs. This is the error message. I have no clue what this means, if it is me doing wrong in the <%@ Application Language="C#" Inherits="MyProject.Global" %> or if I need to change something else as well.

Unable to load one or more of the requested types. The following information may be a subset of the Type/LoaderException information present - inspect with debugger for complete view.
Check assemblies [EPiServer.Search.IndexingService, Version=7.0.1764.1, Culture=neutral, PublicKeyToken=8fe83dea738b45b7] and/or types [EPiServer.Search.IndexingService.IPRange,
EPiServer.Search.IndexingService.FieldProperties,
EPiServer.Search.IndexingService.FieldSerializers.IndexFieldStoreSerializerBase,
EPiServer.Search.IndexingService.FieldSerializers.TaggedFieldStoreSerializer,
EPiServer.Search.IndexingService.FieldSerializers.AclFieldStoreSerializer,
EPiServer.Search.IndexingService.FieldSerializers.PipeSeparatedFieldStoreSerializer,
EPiServer.Search.IndexingService.FieldSerializers.AuthorsFieldStoreSerializer,
EPiServer.Search.IndexingService.FieldSerializers.CategoriesFieldStoreSerializer,
EPiServer.Search.IndexingService.Configuration.ClientCollection,
EPiServer.Search.IndexingService.Configuration.ClientElement,
EPiServer.Search.IndexingService.Configuration.IndexingServiceSection,
EPiServer.Search.IndexingService.Configuration.NamedIndexCollection,
EPiServer.Search.IndexingService.Configuration.NamedIndexElement,
EPiServer.Search.IndexingService.Configuration.NamedIndexesElement,
EPiServer.Search.IndexingService.FieldSerializers.VirtualPathFieldStoreSerializer,
EPiServer.Search.IndexingService.IndexingServiceSettings,
EPiServer.Search.IndexingService.InternalServerErrorEventArgs,
EPiServer.Search.IndexingService.OptimizedEventArgs,
EPiServer.Search.IndexingService.RemoveEventArgs,
EPiServer.Search.IndexingService.AddUpdateEventArgs]. Information from LoaderExceptions property [Could not load file or assembly 'Lucene.Net, Version=2.9.4.1, Culture=neutral, PublicKeyToken=8fe83dea738b45b7' or one of its dependencies. The system cannot find the file specified.].

EDIT: It's the same message as if I would do @inherits MyProject.Global in the razor page.

EDIT: Solved it. Thanks for your help. The last error here I don't know why it happened. Two references had stopped working. The only reason I can think of why they stopped working is because I recently updated to 7.1. Don't know if it is that or something else. Thanks again! EPIServer just got more fun :)